Parathyroid hormone-related protein (PTHrP) is known to widely distribute in the normal human tissues. The physiological functions of PTHrP in normal tissues are suspected to be a paracrine effector. To reveal intracytoplasmic distribution of PTHrP,we firsts established a monoclonal antibody against PTHrP (clone No. : MMUN-034). There are a few parathyroid cells positive for PTHrP,whereas nodular growth of PTHrP positive cell is frequently found in hyperplastic parathyroid glands. In PTr cells, established rat parathyroid cell line, PTHrP was distributed diffusely with net-work like structure similar to that of vimentin. Intracytoplasmic distribution of PTH significantly changed after the stimulation of recombinant PTHrP in PTr cells. That is, parathyroid hormone in PTr cells localized around the nuclei redistributed to the cell membrane 1 hour after PTHrP stimulation. And PTHrP release from parathyroid cells was inhibited by the extracellular calcium. Therefore, PTHrP in the parathyroid gland is suspected to have an important role in the control of cell growth and PTH secretion.PTHrP was also expressed in both T and B lymphocytes. PTHrP in the activated T lymphocytes was localized in the cytoplasmic snout by which T lymphocytes may contact with B lymphocytes. Thus, PTHrP was suspected to have some important roles in the costimulation system between T and B lymphocytes through the regulation of cell contact.